diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -2470,6 +2470,20 @@
     unsigned AbbrevToUse = 0;
     if (C->isNullValue()) {
       Code = bitc::CST_CODE_NULL;
+      const ConstantFP *CFP = dyn_cast<ConstantFP>(C);
+      // PPC_FP128 determines isZero/isNan/isInf using high-order double value
+      // only. If we write NULL bits directly, we may clear low-order double
+      // values unexpectedly.
+      // eg:
+      //    0xM0000000000000000FFFFFFFFFFFFFFFFF
+      // => 0xM000000000000000000000000000000000
+      if (CFP && CFP->getType()->isPPC_FP128Ty()) {
+        Code = bitc::CST_CODE_FLOAT;
+        APInt api = CFP->getValueAPF().bitcastToAPInt();
+        const uint64_t *p = api.getRawData();
+        Record.push_back(p[0]);
+        Record.push_back(p[1]);
+      }
     } else if (isa<PoisonValue>(C)) {
       Code = bitc::CST_CODE_POISON;
     } else if (isa<UndefValue>(C)) {
diff --git a/llvm/test/CodeGen/PowerPC/ppc_fp128-bcwriter.ll b/llvm/test/CodeGen/PowerPC/ppc_fp128-bcwriter.ll
--- a/llvm/test/CodeGen/PowerPC/ppc_fp128-bcwriter.ll
+++ b/llvm/test/CodeGen/PowerPC/ppc_fp128-bcwriter.ll
@@ -1,7 +1,7 @@
 ; RUN: llvm-as < %s -o - | llvm-dis - | FileCheck %s
 
 ;CHECK-LABEL: main
-;CHECK: store ppc_fp128 0xM0000000000000000000000000000000
+;CHECK: store ppc_fp128 0xM0000000000000000FFFFFFFFFFFFFFFF
 
 define i32 @main() local_unnamed_addr {
 _main_entry: